With more mumps infections potentially brewing during Ohio State University’s spring break, officials continue to investigate an outbreak that has sickened at least 16.

While booster shots for healthy people at risk of exposure aren’t routinely recommended by the Centers for Disease Control and Prevention, city health officials have discussed that possibility with federal officials, said Dr. Mysheika Williams Roberts, medical director and assistant health commissioner of Columbus Public Health.

Yesterday, outbreak investigators continued to interview sick students, who are voluntarily isolating themselves, and many are quite ill though none has been hospitalized, she said.

The 16 students known to have the mumps range in age from 18 to 48. The most recent onset of symptoms was on Wednesday, Columbus Public Health said.

Connections beyond enrollment at the university had been elusive as of yesterday, as investigators continued to search for commonalities — such as class schedules or buildings frequented by those infected — to better explain the spread, Roberts said.

Mumps is rarely seen in the United States because of widespread vaccination. Vaccines aren’t 100 percent effective, but when combined with the rare exposure in this country, mumps usually is not a threat.

But if an initial person is infected (sometimes through foreign travel), he or she poses a threat to those whose vaccines didn’t provide full coverage and to those who weren’t vaccinated. Some parents choose not to vaccinate their children, citing concerns about health risks.

Ohio State does not require students to be vaccinated against mumps, though some universities do.

Immunization records have confirmed that seven of the sickened students had both doses and two had at least one, Roberts said. Five others have said they had the vaccine, though no records confirm it. Two have an unknown vaccination status.

Complicating matters and creating potential long-term concerns at Ohio State are two factors: First, people can be infected without feeling sick and unknowingly spread the virus. Second, the incubation period lasts as long as 25 days, meaning a person can be a threat for a long time.

“Whenever you have a long incubation period for a disease, you usually see a prolonged outbreak,” said Roberts, adding that her department and university officials are discussing potential plans for isolation and management of cases to prevent a wider outbreak next week.

Mumps patients are most infectious from a couple of days before swollen glands appear to five days after.

A 2012 study showed some benefit from offering a third dose of vaccine to an at-risk population during a 2009-10 outbreak in New York. A decline in new cases after the booster effort led researchers to conclude that it could help in limited settings.

“We are starting to talk to CDC to see if they have any guidance or recommendations about a third (measles-mumps-rubella) vaccine. It’s still very experimental,” Roberts said. “A lot would be based on the numbers and the severity of the cases.”

Mumps in those who’ve been vaccinated tends to be a milder illness, said Dr. Dennis Cunningham, an infectious-disease expert at Nationwide Children’s Hospital.

The majority of sickened people don’t need hospitalizations or have life-threatening complications, he said.